1. Field of the Invention
The present invention relates to a semiconductor device, a liquid crystal display device and a method of manufacturing a semiconductor device, and particularly relates to a semiconductor device and a liquid crystal display device, in which a contact portion in contact with an interconnection, an electrode or the like has a reduced contact resistance, as well as a method of manufacturing such a semiconductor device.
2. Description of the Background Art
Liquid crystal display devices of a thin film transistor type, which will be referred to as xe2x80x9cTFT-LCDsxe2x80x9d hereinafter, have been improved to achieve larger sizes and higher definition. In accordance with this, interconnections made of alloy, which is primarily formed of aluminum and has a relatively low resistance, have been employed for preventing signal delay on the interconnections such as a gate bus-line.
A method of manufacturing a TFT-LCD in the prior art will now be described by way of example with reference to the drawings. Referring to FIG. 20, an aluminum alloy film (not shown) of about 200 nm in thickness is formed on a surface of a glass substrate 102 by a sputtering method. A predetermined photoresist pattern (not shown) is formed on the aluminum alloy film.
Etching with etching liquid, which is primarily made of phosphoric acid, acetic acid and nitric acid, is effected on the aluminum alloy film masked with the photoresist pattern described above. Thereby, a gate electrode 104b including a gate bus-line as well as a common line 104c are formed in an image display portion A, and a terminal interconnection 104a (i.e., an interconnection 104a on the terminal side) is formed in a terminal portion B.
Referring to FIG. 21, a silicon nitride film 106 having a thickness of about 400 nm is formed by a CVD method of the like on glass substrate 102 so that terminal interconnection 104a, gate electrode 104b and common line 104c are covered with silicon nitride film 106. Then, an amorphous silicon film of about 200 nm in thickness is formed on silicon nitride film 106. Further, an n+-type amorphous silicon film of about 50 nm in thickness is formed.
A predetermined photoresist pattern (not shown) is formed on this n+-type amorphous silicon film. An isotropic etching is effected on the n+-type amorphous silicon film and the amorphous silicon film masked with the photoresist pattern. Thereby, amorphous silicon films 107 and n+-type amorphous silicon films 108 each having an isolated form are formed.
Referring to FIG. 22, a chrome film (not shown) of about 400 nm in thickness is formed by a sputtering method or the like on silicon nitride film 106 so that amorphous silicon film 107 and n+-type amorphous silicon film 108 in the isolated form are covered with this chrome film. A predetermined photoresist pattern (not shown) is formed on the chrome film.
The chrome film thus masked with the photoresist pattern is etched to form drain electrodes 109a and source electrodes 109b. Thereafter, appropriate processing is performed to remove n+-type amorphous silicon film 108 located on each amorphous silicon film 108 which will form a channel region. Thereby, Thin Film Transistors (TFTs) T each including gate electrode 104b, drain electrode 109a and source electrode 109b are formed.
Referring to FIG. 23, a silicon nitride film 110 which covers and thereby protects thin film transistors T is formed, e.g., by the CVD method. A predetermined photoresist pattern (not shown) is formed on silicon nitride film 110.
An isotropic etching is effected on silicon nitride films 110 and 106 thus masked with the photoresist pattern so that contact holes 111a are formed to expose the surfaces of drain electrodes 109a, respectively. Contact holes 111b are also formed for exposing the surfaces of terminal interconnections 104a, respectively.
Referring to FIG. 24, a transparent and conductive film made of oxide such as an ITO (Indium Tin Oxide) film of about 100 nm in thickness is formed on silicon nitride film 110 by the sputtering method or the like so that contact holes 111a and 111b may be filled with this ITO film or the like. A predetermined photoresist pattern (not shown) is formed on the ITO film.
The ITO film thus masked with the photoresist pattern is etched with etching liquid containing hydrochloric acid and nitric acid so that pixel electrodes 113a are formed in image display portion A, and terminal electrodes 113b are formed in terminal portion B. Each pixel electrode 113a is electrically connected to drain electrode 109a, of thin film transistor T. Each terminal electrode 113b is electrically connected to terminal interconnection 104a. 
Then, a glass substrate and a color filter (both not shown) are disposed on the above structure with a sealing material (not shown) therebetween. Liquid crystal is supplied into a space between glass substrate 102 provided with thin film transistors T and the glass substrate covered with the color filter. Further, a drive IC (i.e., IC for driving) is mounted on a predetermined terminal portion. The TFT-LCD is completed through the manufacturing process described above.
In the TFT-LCD, as described above, alloy films primarily made of aluminum are used in the gate bus-lines including the gate electrodes, the terminal interconnections and others. The purpose of this is to prevent signal delays by employing the alloy primarily made of aluminum as materials of the electrodes and interconnections, and thereby reducing the resistances thereof.
In the conventional TFT-LCD, however, oxide aluminum is formed on the interface between terminal interconnection 104a and terminal electrode 113b particularly in the contact portion within contact hole 111b. Such oxide aluminum is probably formed, e.g., due to reaction, which occurs on the interface between terminal interconnection 104a made of the aluminum alloy and terminal electrode 113b made of the ITO film or another transparent and conductive oxide film, due to oxygen plasma processing after formation of the contact holes, or due to natural oxidization occurring as a result of exposure of the substrate to the atmosphere.
Since the oxide aluminum is formed in the contact portion as described above, a contact resistance may take on an extremely high value of 100 Mxcexa9 or more if the contact area is in a practical range. Therefore, good electric contact cannot be achieved between terminal electrode 113b and terminal interconnection 104a so that the TFT-LCD cannot operate appropriately.
Further, the etching liquid, which is used for forming pixel electrode 113a and terminal electrode 113b made of the ITO film, may spread into the structure through pinholes in silicon nitride films 110 and 106. Since the etching liquid contains hydrochloric acid and nitric acid as already described, terminal interconnection 104a and gate electrode 104b made of aluminum alloy may be etched or corroded.
For overcoming the above problems, therefore, such a structure is already proposed, e.g., in Japanese Patent Publication No. 7-113726 that a chrome film or the like is layered over the surfaces of terminal interconnection 104a and gate electrode 104b made of aluminum alloy. The chrome film thus layered provides good electric connection to the ITO film. Also, the chrome film has a sufficient resistance against chemical liquid, and therefore can protect the interconnections and others made of aluminum alloy.
For coating the surfaces of terminal interconnection 104a and gate electrode 104b made of aluminum alloy with another kind of metal film, however, a sputtering device must be provided with a metal target corresponding to such a metal film. For forming the interconnection and others, it is necessary to conduct different kinds of etching which correspond to the film qualities of the metal films, respectively. This increases the manufacturing cost, and also increases the number of manufacturing steps.
The invention has been developed for overcoming the foregoing problems, and first and second objects of the invention are to provide a semiconductor device and a liquid crystal display device, which are provided with electrodes or interconnections allowing easy reduction in contact resistance and having resistances against chemical liquid. A third object of the invention is to provide a method of manufacturing such a semiconductor device.
A semiconductor device according to a first aspect of the invention includes a substrate having a main surface, a first conductive layer and a second conductive layer. The first conductive layer is formed on the main surface of the substrate. The second conductive layer is formed on the main surface of the substrate, and is electrically connected to the first conductive layer. The first conductive layer is formed of layered films having a first layer primarily made of aluminum, and a second layer including aluminum containing nitrogen. The second layer of the first conductive layer and the second conductive layer are in direct contact with each other in a contact portion between the first and second conductive layers, and the second layer in the contact portion has a thickness determined to provide a predetermined contact resistance based on a specific resistance of the second layer.
According to the above structure, since the second layer of the first conductive layer in the contact portion has the predetermined thickness determined corresponding to the specific resistance value of the second layer, the contact resistance can be significantly reduced. As a result, the semiconductor device in which signal delay is prevented is achieved.
Preferably, the semiconductor device further includes an insulating film formed on the substrate and covering the first conductive layer, and a contact hole formed in the insulating film and exposing the surface of the first conductive layer, the contact portion is located within the contact hole, the second layer in the first conductive layer is formed on the first layer, and the second conductive layer is formed on the insulating film and in the contact hole.
In this case, the second layer include the aluminum containing the nitrogen, and therefore can protect the first layer, e.g., from chemical liquid such as etching liquid used for forming the second conductive layer. Consequently, it is possible to suppress corrosion of the interconnections and others while preventing the signal delay.
The second layer in the contact portion has the thickness d satisfying a relationship of 0 less than xcfx81xc2x7d  less than 3xcexa9xc2x7xcexcm2 in the case where the specific resistance xcfx81 of the second layer satisfies a relationship of 50 less than xcfx81xe2x89xa61xc3x97105 xcexcxcexa9xc2x7cm, and satisfying a relationship of 0 less than d less than 3 nm in the case where the specific resistance xcfx81 satisfies a relationship of 1xc3x97105 xcexcxcexa9xc2x7cm less than xcfx81. The predetermined contact resistance R preferably satisfies a relationship of Rxc2x7S less than 100 Mxcexa9xc2x7xcexcm2, where S represents an area of the contact portion. Thereby, the contact resistance can be equal to 100 Kxcexa9 or less, and desirably several kilohms when the contact area is in, a practical range, and therefore the contact resistance in the contact portion can be remarkably reduced.
Preferably, the second layer outside the contact portion has the thickness T larger than that of the second layer in the contact portion.
This structure can reliably prevent chemical liquid such as etching liquid for forming the second conductive layer from spreading into the first layer of the first conductive layer, e.g., through pin-holes in the insulating film. As a result, the first conductive layer can have a good resistance against the chemical liquid.
Preferably, the crystal grain of aluminum of the first layer has a surface orientation of (111).
This structure promotes nitriding of the aluminum of the first layer, and a surface portion of the first layer having an appropriate thickness is nitrided in the process of forming the second layer including aluminum containing nitrogen. This improves the state of joining between the first and second layers in the interface, and reduces the contact resistance.
Preferably, the thickness T of the second layer satisfies a relationship of 0 less than d less than 20 nm in the case of the specific resistance xcfx81 of the second layer satisfying a relationship of 50 less than xcfx81xe2x89xa61xc3x97105 xcexcxcexa9xc2x7cm. 
In this case, the second layer outside the contact portion has the thickness T smaller than 20 nm. Thereby, eaves of the second layer, which is formed due to difference in film quality between the first and second layers during formation of the first conductive layer, can have a more gentle form. Consequently, the second conductive layer, which is formed on the first conductive layer with the insulating film therebetween, can be prevented from being broken on the stepped portion formed by the eaves.
In the case of the thickness T satisfying a relationship of Txe2x89xa720 nm, it is preferable that the insulating film has the thickness larger than 1 xcexcm.
Owing to this increased thickness of the insulating film, it is possible to suppress breakage of the second conductive layer even when the second layer forms the eaves.
The insulating film described above preferably includes a transparent resin film, and the semiconductor device can be applied, e.g., to a liquid crystal display device or the like requiring light transparency.
More preferably, the second conductive layer includes a transparent conductive film.
In this case, the semiconductor device can be applied to the liquid crystal display device or the like.
According to a second aspect of the invention, a liquid crystal display device includes a transparent substrate having a main surface, a first conductive layer, an insulating film, a contact bole, and a transparent second conductive layer. The first conductive layer is formed on the main surface of the substrate. The insulating film is formed on the substrate and covers the first conductive layer. The contact hole is formed in the insulating film, and exposes the surface of the first conductive layer. The second conductive layer is formed on the insulating film, fills the contact hole, and is electrically connected to the first conductive layer. The first conductive layer has a lower layer portion primarily made of aluminum, and an upper layer portion layered on the lower layer portion and including aluminum containing nitrogen. The contact hole exposes the surface of the upper layer portion. The upper layer portion in the contact portion within the contact hole has a thickness determined to provide a predetermined contact resistance based on a specific resistance value of the upper layer portion.
According to this structure, since the upper layer portion of the first conductive layer in the contact portion has the predetermined thickness which is determined based on the specific resistance value of the upper layer portion, the contact resistance can be significantly reduced. Since the upper layer portion includes aluminum containing nitrogen, it is possible to protect the lower layer portion from chemical liquid such as etching liquid used for forming the second conductive layer. Consequently, it is possible to provide the liquid crystal display device, in which signal delay can be easily prevented, and corrosion of the interconnections and others can be suppressed.
The upper layer portion in the contact portion has the thickness d satisfying a relationship of 0 less than xcfx81xc2x7d less than 3xcexa9xc2x7xcexcm2 in the case where the specific resistance xcfx81 of the upper layer portion satisfies a relationship of 50 less than xcfx81xe2x89xa61xc3x97105 xcexcxcexa9xc2x7cm, and satisfying a relationship of 0 less than d less than 3 nm in the case where the specific resistance xcfx81 satisfies a relationship of 1xc3x97105 xcexcxcexa9xc2x7cm less than xcexa9. The predetermined contact resistance R preferably satisfies a relationship of Rxc2x7S less than 100 Mxcexa9xc2x7xcexcm2, where S represents an area of the contact portion. Thereby, the contact resistance can be equal to 100 Kxcexa9 or less when the contact area is in a practical range, and desirably is equal to several kilohms or less, and therefore the contact resistance can be remarkably reduced.
According to a third aspect of the invention, a method of manufacturing a semiconductor device includes the following steps. Processing is performed to form on a substrate a first conductive layer having a lower layer portion primarily made of aluminum, and an upper layer portion layered on the lower layer portion and made of aluminum containing nitrogen. Processing is performed to form on the substrate an insulating film covering the first conductive layer. A contact hole exposing the surface of the upper layer portion is form:ed in the insulating film. Processing is performed to form on the insulating film a second conductive layer electrically connected to the upper layer portion exposed on the bottom of the contact hole. In the step of forming the contact hole, the upper layer portion in the contact portion is determined to have a predetermined thickness so as to provide a predetermined contact resistance based on the specific resistance value of the upper layer portion.
According to this method, since the predetermined thickness of the upper layer portion in the contact portion is determined based on the specific resistance of the upper layer portion in the step of forming the contact hole, the contact resistance can be significantly reduced. Since the upper layer portion includes aluminum containing nitrogen, it is possible to protect the lower layer portion of the first conductive layer from chemical liquid such as etching liquid used for forming the second conductive layer. Consequently, it is possible to manufacture the semiconductor device, in which signal delay can be easily prevented, and corrosion of the interconnections and others can be suppressed.
Preferably, the upper layer has the thickness d satisfying a relationship of 0 less than xcfx81xc2x7d less than 3xcexa9xc2x7xcexcm2 in the case where the specific resistance xcfx81 of the upper layer portion satisfies a relationship of 50 less than xcfx81xe2x89xa61xc3x97105 xcexcxcexa9xc2x7cm, and satisfying a relationship of 0 less than d less than 3 nm in the case where the specific resistance xcfx81 satisfies a relationship of 1xc3x97105 xcexcxcexa9xc2x7cm less than xcfx81. Thereby, the contact resistance can be equal to 100 Kxcexa9 or less when the contact area is in a practical range, and desirably is equal to several kilohms or less, and therefore the contact resistance can be remarkably reduced.
Preferably, the upper layer portion is formed in a nitrogen atmosphere by a sputtering method under the conditions of 0.1 less than F/D less than 10 ml/nm where F represents a flow rate of the nitrogen supplied into the atmosphere in contact with the substrate, and D represents a growth rate of the upper layer portion (conditions of 0.1 less than F/D xe2x89xa610 ml/nm will be referred to as conditions A, and conditions of 1 less than F/D less than 10 ml/nm will be referred to as conditions B, hereinafter).
Under the above conditions A, the upper layer portion has a relatively low specific resistance, and the predetermined contact resistance can be achieved while keeping a large margin of the thickness of the upper layer portion. Under the conditions B, the upper layer portion has a relative high specific resistance, and a resistance can be kept against chemical liquid such etching liquid, e.g., for forming the second conductive layer.
Under the conditions A described above, since the margin of the thickness of the upper layer portion is large, it is preferable that the growth rate D of the upper layer portion satisfies a relationship of 3 less than D less than 60 nm/min.
Under the conditions B, however, the specific resistance is relatively high so that the thickness achieving the predetermined contact resistance can be selected only from a relatively narrow range. In this case, the growth rate D of the upper layer portion preferably satisfies a relationship of 3 less than D less than 10 nm/min.
Preferably, formation of the lower layer portion starts after the pressure decreases to or below 10xe2x88x923 Pa.
This feature can remarkably suppress formation of aluminum oxide between the lower and upper layer portions.
Preferably, the substrate is exposed to an atmosphere containing oxygen in a concentration of 10xe2x88x9210 mol/l or less for a period from start of formation of the lower layer portion to end of formation of the upper layer portion.
In this case, it is likewise possible to suppress reliably the formation of aluminum oxygen between the lower and upper layer portions.
Preferably, the upper layer portion is formed in an atmosphere containing a nitriding gas nitriding aluminum. The nitriding gas may preferably contain a gas containing at least one of nitrogen, ammonia, hydrazine and hydrazone.
Preferably, a scan magnetron sputtering device is used for the first conductive layer.
According to the scan magnetron sputtering device, a distribution of thickness of the first conductive layer formed on the substrate can be controlled by an oscillating speed of a magnet, and therefore the thickness of the first conductive layer within the surface of the substrate can be easily controlled.
Preferably, the step of forming the contact hole includes supply of a nitriding gas nitriding aluminum before the lower layer portion is exposed.
In this case, even when the etching for forming the contact hole removes the upper layer portion to expose the surface of the lower layer portion, a nitrogen-containing aluminum film is formed at the surface of the lower layer portion owing to the supply of the nitriding gas. Thereby, increase in the contact resistance can be suppressed.
Preferably, the step of forming the first conductive layer includes a step of patterning the first conductive layer by dry etching.
In this case, it is possible to eliminate eaves of the upper layer portion, which may be caused due to difference in film quality between the upper and lower layer portions, in contrast to the case of performing wet etching for patterning. As a result, the second conductive layer formed on the first conductive layer can be prevented from being broken on a stepped portion of the first conductive layer.
It is desired that the nitrogen used as the nitrifying gas is in advance mixed and diluted with an inert gas within a gas cylinder.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.